Rheostat



Aug. 14, 1928.

A. F. C. LoTz RHEosTAT vFiled oet. 15. 1925 4 she sheet 1 7////// 5 M /37 f 45 W0 5.364

aww/'Mba Aug. 14, 1928. 1,680,744

A. F. c. Lofrz mmosm'r 'Filed oct. 15, 1925 4 sheets-sheet 3 `Q Gif/7 u@ 7177/7.

Aug. 14, 1928. 1,686,744

A. F. C. LOTZ RHEOSTAT Filed Oct. 15, 1925 4 Sheets-Sheet 4 Patented Aug. 14, 1928.

UNITEDs'm'rias-` PAT-ENT OFFICE.

ALFRED E. C. LoTz, OF CHICAGO, ILLINOIS, ASSIGNOR To ELECTRICAL. ENGINEERS EQUIPMENT COMPANY,A or CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

RIIEosTAT.

Application led Oct-Ober 15, `1925. Serial No. 62,522. f

My invention relates to rheostats and has especial reference to a rheostat having particular utility in radio Work. A

The present invention maybe characterized as an improvement upon the device disclosed in my Patent No. 1,625,479, Apr. 19, 1927, and its objects are the provision of a generally improved and simplified construen tion that may be economically produced and conveniently Operated, and which will give a smooth, quiet, stepless, fine and accurate adjustment without any undesirable `action or characteristics.

According to my present invention I provide for minimizing the inherent resistance, that is, the minimum resistance of the dcvice. l

I alsoprovide for minimizing the stresses upon the resistance. conductor ofthe device and upon the connectionor joint between that conductor and the operating element or elements, vas the case may be.

IV also provide for improving the joint or connection between the insulating Vdrum contact andthe drum, andan improved contact between the drum'contact and its cooperating contact.

I also provide for relieving the case or housing of any movement limiting or stopping function for the rider or` circuit open-V ing or controlling means and for relieving the housing and driving shaft of any stresses accompanying such a function.

I also provide a symmetrical Contact arm `or spring and end wall structure which may be assembled without predetermining its po? sition and an improved mounting for hold-l ing the contact arms or springs tirmlyin position.

I also provide an improved journal for the driving shaft in the end wall of the case, an improved floating mounting of the driving gear, and an improveddriving connection between said gear and the driving j Sima. i

I also provide an improved seating of the case or cover inv its end walls and an 1my proved arrangement and anchoring of the companying drawings a particular embodi`- ment of the invention.

In the drawings Figure 1 is a side elevational view with the case or frame in section; y Y i Fig. 2 is a section taken substantially on' the line 2 2 of Fig. l;

Fig. 3 i

is asection taken on substantially the plane of the line 3 3 of Fig. 2;v i

Fig. 4 is a section taken von substantially the plane of the line 4 4 of Fig. 3; 1 Fig; 5 is a` section taken on substantially the plane of the line 5 5 'of Fig. 3; i

Fig. 6 is an elevational view of the backv end ofthe device;

Fig. 7 is a section taken on substantiallyl Fig. 1l is across section through the re- I sistance conductor taken on the line l1 11 of Fig. 10;

Fig- 12 is a cross section through the terminal portion of the resistance Conductor taken on the line 12--12 of Fig. 10;

Fig. 13 is a detail section taken on the line 13 13 of Fig. 3; I v

Fig. 14 is an isometrio-view'of vthe driving shaft journal which is mounted in the front end; j Y i Fig. 15l is a fragmentary isometric view of the driving shaft showingthe means for connecting the driving gear for rotation therewith and f Fig. 16 is an isometric view of the driving gear which is mounted uponthe driving shaft. I Y

Merely as illustrative of the .relative di-y mensions of a commercially practical.` embodiment of the'device lwhich I at present y construct, vthe device shown in the .ao-l

-companying drawings is'substantially twice the size of that device. 4This is merely illustrative and is in no wise intended to limit lthe size'or proportions of the invention.v

Referring to the drawings, the device is enalosed within an nhleng' ease the end walls or front wall and back 6, which may be of suitable insulating material. The back 6 is shown in the forni of a detachable cover. The walls 5 and 6 may be oblong with their ends rounded or semicircular, each end 5 and 6 having a marginal flange 7 and in the inside or opposing surfaces of the end walls 5 and 6 are marginal grooves 8 about the flanges 7.

A cover or case 10:. which may comprise a relatively thin sheet or strip of transparent material, for example7 Celluloid or isinglass material such as Pyralin is folded to conform or fit within the flange 7 with its opposite or free ends meeting or overlapping. rl`he opposite edges of the cover l() lit within the liangcsf'l' and seat in the grooves 8 so that the cover is held firmly and properly in place by the means which holds the end walls 5 and 6 together.

Rotatably mounted within the cover 1() and between the end walls 5 and 6 with their axes substantially parallel is an insulating cylinder orV drum 12 and a conducting or short circuiting cylinder 13. n

The cylinder 12 may be formed of insulating .material such as a phenol condensation compound and it comprises an axially bored hub liland a surrounding cylindrical wall 15 having an open end 16 and aV closed end 17. Integral webs ,18 may be provided between the hub 14 and the lwall 15. The cylinder 1Q is rotatably journalled upon a shaft 19, the opposite ends of which are reduced to provide siioulders which abut and space'the end walls 5 and 6. The reduced 'endsef the shaft 19 are threaded and these threaded ends extend through openings in the end walls 5 and 6 and engage in nuts 20, which when tightened or brought upcla'mp the end walls 5 and 6 firmly together. Suitable washers maybe interposed between the end walls 5 and Gand the nuts 20, as shown. The cylinder 12 is thus mounted to rotate on the shaft 19 and the shaft 19 is rigidly secured in the case and spaces and joins the end walls thereof. Y Y

The cylinder 13 maybe of metal or suitable cenducting material, such as `brassror copper, and itcomprises an axially bored hub 24 and a surrounding cylindrical or annular wall 25 having an open end 26 and a closed cndl. The wall 25 is provided internally with the longitudinally extending integral lug or shoulder 28 and the hub 24 terminates short of the open end of the cylinder 13. The cylinder 13 is rotatably journalled upon a shaft 29, the opposite ends of which are reduced tok forni shoulders which abut and spacek the end walls 5 and 6 symmetrically upon the opposite side of the driving shaft 30. As rwith the shaft 19, 4the Vreduced'endsfof the shaft 29'are threaded and these threaded ends extend through openings in theend walls 5 and 6 and engage vends 5 and 6 and the nuts 32.

in nuts 32 which clamp the end walls 5 and 6 firmly together. As before7 suitable wasliers are rpreferably interposed between the The cylinder 13 is thus mounted to rotate on the shaft Q9 and the shaft 29 is rigidlysecured in the case, and with the shaft 19` provides a Vsymmetrical spacing and joining of the ends 5 and 6.

The closed end 1'1" of the cylinder or drum 19. has an annular recess 35 in which is secured an annular contact or comniutator ring The outer end of the conducting or short circuitinf.;- drum 13 forms a contact surface for the drum 13.

The rheostat or resist-ance element comprises a strand of line, relatively high resistance wire 3T, such as van alloy, niclirome7 or the like. One end of this wire or conductor 3T is wrapped on the drum 12 with itsadjae cent end turned in V.through a slot or recess 36, and wrapped on the projecting end of the contact ring 36. That portion of the wire 3.7`wliicli is wrapped upon the contact ring 36 is soldered or otherwise Vconnectid electrically andlnechanieally to the ring 36 at 39.

The opposite end of the conductor 37 is wrapped upon the cylinder 13 with its end turned in through a radial opening- Gand knotted at i2 to anchor it to the cylinder 13. The extei'nalsurface or periphery of the insulating cylinder 12 is threaded or grooved spirally at 43 to accommodate the 'turns of the wire 37, and to space and insulate them from each other. AThe external surface or periphery of the conducting cylinder 13 yis threaded or grooved spirally at Llll intl e same direction to accurately arrange the turnsI of the wire 3T thereon, and te guide the wire properly to and from the cylinder l2.

'At one end of the wire 37 preferably has a dead turn or'two on the drum 12, ythat is7 a turn or two which remains onA thedruni in the complete upwrapped position of the drum, and at itsvopposite end the wire37 preferably has a similar dead turn or two on the drum 13. between the respective drums and the opposite ends of the conductor 37 and relieves the joints or oonnections'of .the terniinals of the wire 37 with the ring 36 and drum 13, respectively, of any stresses at the limits of rotation of the drums. j

The opposite ends of the wire 37 have terminals or circuit connections for connecting the device serially or otherwise in the desired circuit. 'These comprise spring contact or brush arms 18 and 50. One of these arms is secured to the end wall 6 by a screw 52 which extends through and engages in a nut 53 which, Vwith an additional nut 54, provides a binding post to which the desired circuit conductor may be conveniently connected mechanically and electrically.` The This provides belt 'friction i mounting of the other contact arm upon the iii) substantially' the same.

end wall 6 and its circuit connection are Spring washers are preferably interposed between the end 6 and the nuts to keep the Contact arms tightly clamped to the back or cover 6;

The contacting ends of the arms 48 and 50, which have wiping contact on the ring 36 and drum 18. respectively` are preferably splitor divided longitudinally at 58 to form spring ends for good, firm and'maximum contact with the ring 86 and drum 13 at all times. y' y The contact arms 48 and 50 are mounted with their lengths extending longitudinally of the hack 6 and preferably with one disposed on each side of thedriving shaft 30.

AThis provides a compact and symmetrical arrangement. The arms 48 and 50 are carried by the back 6 and removed and as sembled therewith, the symmetrical dispositionof the arms thereon making a predetermined positioning of the back in assembling unnecessary becausev which ever way the back is applied one arm will engage the Aring 36 and the other arm will engage the drum 18. Either arm will cro-operate with either drum and when one arm is in cli-operation with one drum, the other arm co-operates with the otherdrum.

For the purposeof holding the arms firmly in place and preventing accidental turning on their posts or screws 52, the back or end 61preferably'` has a pairof integralA projecting lugsorshoulders co-operating with the anchored ends of the arms 48 and. 50, as shown in Fig. 6.

For the purpose'of firmly securing the ring 36 in the recess 35, I tin the washer or ring 36, or coat it'with a suitable relatively soft conducting coating.` The washer may be of brass,for example, and it may be pressed into the recess in the end of the drum 12. lThis tinning or coating provides firm adhesion of the washer lto the insulating drum 12, and it provides a soft conta-ct surface, which upon operation of the device I find is quickly grooved by the contact arms `48 or 50, this grooving of the arm thereinto forming a good, maximum contact at all times. tion of the wire B'tothe` ring is also hereby avoided. The `contact end of the drum 18 may be similarly tinned or coated.

The driving shaft 30 extends between the cylinders or drums 12 andv lfwhich makes for compactness and symmetry. The inner or back end of theshaft() is reduced at 65 and this reduced end is rotatably journaled in the back cover wall 6. The forward part of the shaft 30 is enlarged at 66 and the enlarged shaft part 66 is rotatably journaled in a'bearing .bushing or sleeve 68. The:

bushing 68 comprises an externally threaded cylindrical sleeve or thimhle having Van enshaft.

Subsequent hand tinning for connecylarged non-circularV head '70V yof `square orV other vpolygonal formation, forl example, which may be formed integral with the bushing sleeve. .The inside surface of the wall 5 has a non-circular recess 72 conforming to the head 70 and 'adapted to receive or accommodate same, the engagement of the head 70 in this recess/F2. holding the bushing rigidly against turning in the wall 5 and limiting its forward or Aoutwardmovement'therethrough. A nut 7 3 threaded eX- ternally upon the bushing 68 up into engagementwith the wall 5,' binds the bushing rigidly in said wall. s' y VThe outer endof the shaft 30 may be' of suflicient length to pass through an insulating panel or plate'75 or other support, andy insert or sleeve 79 secured axially in the hubV portion of the knob. vThe i insert 79 is threaded to accommodate a radial screw 81 which threads through the sleeve 7 9 and into engagement with the shaft 30 to secure the knob rigidly thereon. Y Y

Between the front cover'or end wall 5 and the forward end Vofthe cylinders or drums 12,13, `the driving shaftBO has secured thereto a drivingl gear or pinion 82. The pinion 82 has a non-circular recess 83, as shown in Fig. 16, whichmay be square, and integral with the driving shaft 80 is a non-circular portion 84 of a contour corresponding to the Vrecess 83.` In VVassembling the gear 82, is slipped upon the `shaft 80 with the non-circular portion 84 of the shaft tting in the recess 88 and fixing the gear on the shaft for rotation therewith.. vConnecting pins or keys between-the gear and shaft, which are undesirable because of the .relatively smalldimensions' of the parts,`are thus avoided and, at thefsame time, a floating `mounting of the gearw82 between the end wall 5 and drums 12, 13 is secured, the gea-r seing also conveniently removable from the The driving gear '82 is disposed between and meshes with a pair of gears 86 and 87,

y one for each of thef cylinders or drums 12 ygear 86 maybe formed by cutting the teeth directly yin theV end ofthe cylindrical insulatingwall 15 of the drum 12, which makes al rigid integral unit in which attachment means Vor connections between the gear and ldrums are eliminated.

The gear 87 has an vaxiallylbored hiib,A

vloosely f rotatable on the shaft 29, and projecting from the inner surface of the gear i this spring is turned out at 91 into engagement with the lug 28. The opposite end is turned out at 92 for engagement or co-operation with the lug 89, providing a yieldable or take-np connection between the drum 13 and the gear 82, for maintaining the resistance wire 37 always properly tensioned or tightened.

In winding the resistance conductor in the assembly of the device, the lugs 28 and 92 may be first placed in engagements() that the gear 87 and drum 13 are driven positively together. Upon completing the winding the lug 92 may be sprung past the lug k28 in the direction of tensioning of the spring (Figure 8), s0 that thereafter in the operation of the device the gear 87 turns the drum 13 through the spring 90. The spring 90 is shown tensioned in Figure 8 by the relative movement Vwhich accompanied separation of the lugs 28 and 92 in a clockwise direction in Figure 8. The resistance conductor 37 is thereby maintained taut und properly tensioned at all times. i y

For the purpose of opening the controlling circuit when the resistancel is entirely in circuit and for closing it when operation is desired and it is Vdesired to reduce the resistance, an abutment block or rider 95 is provided.l -This block or rider 95 may be ofy insulating material having a metal insert 96 threaded upon the threaded portion of the shaft 30. The rider 95 has depressions in its opposite sides conforming generally to the peripheries of the drums 12 and 13 between which it lits and is held against Vturning and guided between the drums.

The opposite .ends of the rider 95 extend radially from the shaft between the drums for engagement with the contact arms 48, 50, as the rider reaches the limit of its movement toward the block 6. When the driving shaft has been turned to place the drums with substantially the entire resistance effective, the rider 95 will have shifted along lche shaft 30 to bring its arms 98 against the contact arms 48, 50, and to Vliftor rdis-r engage said arms 48, 50 from Vcontact with the ring 3G and drum 13, opening the controlled circuit. Vhen the knob 78 is turned in the. opposite direction, the lirst movement or rotation of the shaft causes withdrawal d of the rider 95 from the contact arms 48, 50

projecting radially opposite ends therefrom. The provision of a stop on the shaft relieves the case of any rider stopping purpose and thereby of any stresses or ypressures which might accompany such a purpose. It also relieves. the driving shaft 30 and threads thereon of any stresses incidental to the stopping or limiting of the movement of the rider.

From the foregoing it will now be apparent that the resistance conductor 37 is adapted to. be 'transferred from one drum to the other by turning or rotating the drums. Then substantially all of the conductor 37 is on the drum 12, substantially the entire resistance is in circuit, whereas when the conducting drum 13 is in its completely wound condition with the drum 12 unwound, the minimum resistance is in circuit. With the insulating drum wound and the device operated to transfer the resistance conductor to the contact drum, the conductor is short circuitcd as it passes on to the conducting drum, and this decreases the resistalice in the circuit. Y

For the purpose of minimizing the inherent or minimum resistance of the device, I provide for decreasing the resistance of that portion of the terminal of therwire 37, which connects the contact on the drum 12 with the drum 13 when the drum 12 is unwound.

This may be done by laying a length of wire (Figs. 10 and 12) or any other suitable conducting strip of relatively great conductivity, such as copper, along the insulating drum terminal of the high resistance wire 37 and sweating, soldering, or otherwise securing it along and in parallel loo with the terminal of the Wire 37. Thus,V

when the drum 12 is nnwonnd and substantially the entire resistance is short-circuited by thedrum or cylinder 13, the Contact 36 and cylinder 13 are connected by a terminal of high conductivity, so that 'the resistance is less than the inherent" resistance of a length of the wire 37 suiiicient to connect the drums. i

I do notv intend to be limited to the precise details shown and described.

I claim 1. vIn a resistance device, the combination of a drum, a Contact on said drum, a resistance conductor connected to said contact and adapted for winding upon and unwinding vfrom the drum, and means of relatively high conductivity along the effective terminal portion of said resistance conductor for decreasing the .resistance of said terminal Vportion beyond the normal resistance of said conductor.

2. Ina resistance device, the combination of an insulating drinn, a short circuiting drum, a resistance conductor on said drums, means for shifting the conductor from one of said drums to the other, and means of relatively high conductivity airing the effective' insulating drum terminal of said resistance conductor for decreasing the inherent 4resistance of said conductor When saine is in maximum short circuit position.

3. In a resistance device, the combination of an insulating drinn, a short circuiting drum, a resistance conductor on said drums, means for shifting the conductor from one of said drums to the other, a contact on the insulating drinn, and a terminal of relatively high conductivity for said resistance conductor, said terminal connecting the short cireuiting drum and the insulating y drum contact when the resistance conductor is substantially entirely upon the short circuiting drum.

4. In a device of the class described, the combination of an insulating cylinder, a shortcircuiting cylinder, resistance means carried by said cylinders, separable contacts for said resistance means, a shaft for turning the cylinders to transfer said resistance means from one to the other, means operable along said shaft for separating said contact means and means on the shaft for limiting the movement of said last means.

' 5. In combination, a housing including end Walls,` a rheostat within the housing and including rotatable drums,fshafts rotatably supporting the drums and having reduced Vterminals passing through said Walls, theV Walls being spaced apart by the shafts and having grooves in their inner faces, a inember forming a closure Wall ,extending between the end Walls with its edges seatingV in said grooves, and means cooperating with the terminal elements of the shafts and the body portions of said shafts for securing the end Walls against relative movement.

In Witness whereof, I hereuntosubscribe my name this 13 day of October, 1925.

ALFRED F. C. LOTZ. 

